Acute kidney injury (AKI) is a major determinant of mortality and morbidity in hospitalized veterans. Understanding the pathophysiology of AKI is essential for the development of therapy. This application proposes to study the role of Tamm-Horsfall protein (THP) in AKI. This protein has unclear functions and is expressed exclusively in thick ascending limbs (TAL) of the kidney. The immediate goal of this research is to characterize a novel protective role of THP in kidney injury and inflammation. The PI's long term goal is to understand how the role of THP can be modulated during AKI for preventative and therapeutic purposes. The central hypothesis is that Tamm-Horsfall protein regulates the inflammatory response triggered by ischemic injury in the outer medulla; an effect that requires an interaction of THP with the surrounding tubular elements. This hypothesis has been formulated on the basis of strong preliminary data produced by the PI showing that THP is protective in AKI and is associated with less inflammation and injury to S3 segments, which are neighboring tubules to TAL in the kidney outer medulla. The following specific aims will be used to investigate this hypothesis. Aim 1 will define the interaction between THP and proximal tubules in ischemic injury, thereby supporting a direct THP-S3 interaction. This aim will define the basolateral path for THP release from TAL and the significance of its interaction with receptors on S3 segments Aim 2 will identify specific inflammatory pathways in kidney injury that are modulated by THP. The goal is to establish that the protective effect of THP is in part through the inhibition of a specific inflammatory chemokine pathway. This research will involve the use of THP knockout and wild type mice. The animal model used for AKI is renal ischemia-reperfusion injury achieved through renal pedicel clamping. In vitro studies will involve cell lines for proximal tubules and thick ascending limbs. Other techniques used in this work include: Immunofluoresence confocal microscopy, immuno-gold electron microscopy, flow cytometry, real time-PCR, silencing RNA, western blot, laser capture microdissection and in-situ hybridization. This research is innovative, because it will uncover novel regulatory functions for THP that may be relevant not only in kidney injury but also in other forms of acute or chronic renal disease. Future strategies that enhance the role of THP in the kidney will be of important therapeutic significance.